Luminescent solar concentrators (LSCs) generally consist of transparent polymer sheets doped with luminescent species. Incident sunlight is absorbed by the luminescent species and emitted with high quantum efficiency, so that the emitted light is trapped in the sheets and travels to the edges where it can be collected by solar cells. Unlike regular solar spectrum, the emission spectrum of LSCs based on Lumogen Red dye red shifts and concentrates to a small range of wavelengths (600nm to 700nm). Therefore, hydrogenated amorphous silicon (a-Si:H), whose bandgap is around 750nm, can absorb the emission light without many thermalization losses.
Due to the low diffusion lengths in a-Si:H, thin absorbing layer should be applied, causing insufficient light absorbance. In this letter, we propose a structure that coupling nanostructured plasmonic back contact to LSC solar cell. After optimization, numerical results show that the photocurrent intensity increases by a factor of 1.30 compared with LSC solar cells with randomly textured back contacts. In contrast, when illuminated by one Sun, the photocurrent for textured cell compares to that for nanostructured cell.
The remarkable photocurrent enhancement in LSC cells is attributed to two main reasons. First, the wavelengths, where nanostructured cell shows higher absorbance compared with textured one, are identical with the emission peak of LSC. Second, the light interferences constructed in flat cells, which cause the absorbance curve to red shift and match with the emission spectrum, are depressed in textured cell, but are maintained in nanostructured cell. The second reason is described in detail.